Mixtures for coating metallic surfaces

ABSTRACT

A method for coating a metallic surface by contacting it with an aqueous copolymer dispersion, wherein the aqueous copolymer dispersion comprises an effective amount of magnesium ions and phosphate or phosphonate ions, the copolymers present in the dispersion being constructed from the following components: (A) from 20 to 95 weight % of monoethylenically unsaturated hydrocarbons and/or hydrocarbons having two conjugated double bonds, (B) from 5 to 80 weight % of monoethylenically unsaturated monomers which contain acid groups, and/or anhydrides or salts thereof. Further provided are metallic surfaces coated with such copolymers, and the use of such aqueous copolymer dispersions to coat metallic surfaces.

The present invention relates to methods for coating metallic surfacesby bringing the metallic surface into contact with aqueous copolymerdispersions. The invention further relates to copolymer-coated metallicsurfaces and also to the use of aqueous copolymer dispersions to coatmetallic surfaces.

Further embodiments of the present invention can be found in the claims,description, and examples. It will be appreciated that the features ofthe subject matter of the invention that have been identified above, andthose still to be elucidated below, can be used not only in therespective combination specifically indicated but also in othercombinations as well without departing from the scope of the invention.Preferred and especially preferred embodiments of the present invention,respectively, are more particular those embodiments in which all of thefeatures of the subject matter of the invention have the preferred andespecially preferred definitions, respectively.

The coating of surfaces by aqueous copolymer dispersions is known.

WO 2004/108601 A1 describes the use of aqueous dispersions comprising atleast one at least partly neutralized ethylene copolymer wax, selectedfrom those ethylene copolymer waxes which comprise as comonomers incopolymerized form (A) 26.1 to 39 weight % of at least one ethylenicallyunsaturated carboxylic acid and (B) 61 to 73.9 weight % of ethylene, andthose ethylene copolymer waxes which comprise in copolymerized form (A′)20.5 to 38.9 weight % of least one ethylenically unsaturated carboxylicacid, (B′) 60 to 79.4 weight % of ethylene, and (C′) 0.1 to 15 weight %of at least one ethylenically unsaturated carboxylic ester, asauxiliaries for wastewater treatment. The partly neutralized ethylenecopolymer waxes are at least partially neutralized with a basicsubstance, preferably an amine. The basic substance may also be acarbonate and/or hydrogencarbonate of an alkali metal.

WO 2008/092853 A1 describes a method for coating surfaces by treatingthem with a substantially paraffin-free formulation which comprises acopolymer at least partly neutralized with an alkali metal and made fromethylene and 25.5-35 weight % of an ethylenically unsaturated carboxylicacid. The formulation further comprises at least one nonionic or anionicsurfactant, at least one defoamer, and optionally further components.The basic component may also be a carbonate and/or hydrogencarbonate ofan alkali metal.

WO 2007/137963 A1 describes a method for coating plastics or metallicsurfaces with an aqueous dispersion of ethylene copolymers having amolar mass in the range of 2000-20 000 g/mol, comprising incopolymerized form 15.5-19.9 weight % of an ethylenically unsaturatedcarboxylic acid, and comprising at least one base, the coated surfacesbeing provided with at least one further coat. Examples of the selectedbase are alkali metal salts and more preferably amines.

WO 2006/066824 A1 describes a method for coating metallic surfaces witha copolymer of olefins and/or dienes, acidic monomers, and also,optionally, further monomers, the metal surfaces being contaminated withoil and/or grease and the contamination not being removed prior tocoating. The polymers used are neutralized by a base; preferred metalcations designated include Mg²⁺ ions. The use of phosphates, andespecially of magnesium phosphate, is not mentioned, however.

WO 98/10023 describes the use of aqueous polymer dispersions comprisinga polymer made from an olefin and from an acidic comonomer, at least onecolorant and/or a corrosion inhibitor to protect metallic surfacesagainst corrosion. The corrosion inhibitors used are preferably pigmentswhich are insoluble in the aqueous phase and which limit thetransparency and surface properties of the films.

The above-described dispersions are still deserving of improvement inrelation to corrosion control of metallic surfaces, especially withregard to the passivation of surfaces comprising steel and/or zinc orzinc-containing alloys.

It was an object of the invention to provide an improved method fortreating metallic surfaces that can be employed with particularadvantage in the passivation of surfaces comprising steel and/or zinc orzinc-containing alloys.

As is evident from the disclosure content of the present invention,these and other objects are achieved by means of the various embodimentsof the preparations of the invention.

One subject of the invention is therefore a method for coating metallicsurfaces by bringing the metallic surface into contact with an aqueouscopolymer dispersion, wherein the aqueous copolymer dispersion comprisesan effective amount of magnesium ions and phosphate or phosphonate ionsor mixtures of phosphate and phosphonate ions, the copolymers present inthe dispersion being constructed from the following components:

-   -   (A) from 20 to 95 weight % of monoethylenically unsaturated        hydrocarbons and/or hydrocarbons having two conjugated double        bonds,    -   (B) from 5 to 80 weight % of monoethylenically unsaturated        monomers which contain acid groups, and/or anhydrides or salts        thereof.

Here, the amount of components (A) and (B) is based on the total amountof components (A) and (B). The total amount of components (A) and (B)here is 100 weight %. The components (A) are present preferably in therange from 20 to 95 weight % and (B) in the range from 5 to 50 weight %.

Surprisingly it has been found that metal surfaces treated with themethod of the invention are significantly more resistant to corrosionthan those in accordance with the prior art.

An aqueous copolymer dispersion for the purposes of the presentinvention is a mixture comprising water and copolymers. The water hereis present in an aqueous solvent mixture, with the aqueous solventmixture being composed substantially, more preferably completely, ofwater. The copolymer may be present in dispersion, in emulsion or elseas a molecular solution in the aqueous solvent mixture.

The aqueous solvent mixture contains preferably from 75 weight % to 100weight % of water. Besides water, the aqueous solvent mixture mayoptionally comprise organic solvents as well. The organic solventspreferably comprise compounds selected from the group consisting ofalcohols, ethers, esters, ketones, and amides. Organic solvents of thiskind are frequently used as an ingredient of paints, and are known tothe skilled person from the prior art. Examples of such solvents arealcohols such as methanol, ethanol, propanol, butanol, phenoxypropanol,or ethylene glycol, ketones such as acetone, methyl ethyl ketone,cyclohexanone, oligomeric and optionally partially etherified alkyleneglycol ethers such as, for example, diethylene glycol, triethyleneglycol, tetraethylene glycol, butyl glycol, butyl diglycol,2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, dimerized butyl glycol,dipropylene glycol n-butyl ether, dipropylene glycol dimethyl ether,esters such as the dimethyl esters of adipic acid, succinic acid, andglutaric acid, and mixtures thereof, 2-ethylhexyl lactate, butylphthalate, dibutyl phthalate, amides such as dimethylacetoacetamide,N-methylpyrrolidone, or N,N-dimethyllactamide. In small amounts it isalso possible to use water-immiscible solvents, examples beinghydrocarbons. The small amounts in this case are selected such that novisible additional phase is formed; the small amount is typically lessthan 5 weight % based on the overall mixture.

The copolymers in the aqueous solvent mixture are present preferably inlargely molecularly disperse form or in the form of a very finedispersion having an average particle size of below 100 nm, determinedby dynamic light scattering in accordance with DIN ISO 13321. This meansthat they do not lead to significant changes in the transparency of theaqueous solvent, let alone to the formation of a sediment.

The copolymers preferably have molecular weights M_(w) (weight average)of above 20 000 g/mol, very preferably of above 50 000 g/mol. Moreparticularly the molecular weights of the copolymers are in the rangefrom 20 000 g/mol to 200 000 g/mol, very preferably from 50 000 g/mol to200 000 g/mol.

In one preferred embodiment of the method of the invention, thecopolymers present in the dispersion comprise as a further component:

-   -   (C) from 0 to 30 weight % of ethylenically unsaturated monomers        different from (A) and (B).

In another preferred embodiment of the method of the invention, thetotal amount of magnesium ions, phosphate ions, and phosphonate ions isin the range from 0.1 to 5 weight %, based on the amount of thecopolymers, preferably in the range from 0.2 to 3.5 weight %, morepreferably in the range from 0.4 to 2 weight %, very preferably from 0.6to 1.6 weight %.

For the purposes of the method of the invention, the magnesium ions andphosphate or phosphonate ions are preferably added in the form of a saltcontaining magnesium phosphate or magnesium phosphonate to the aqueouscopolymer dispersion. Preferred salts in this context are magnesiumphosphate, magnesium phosphonate, magnesium phosphate octahydrate, orother hydrates of these salts. The compounds may also be in partlyprotonated form, for example as hydrogenphosphates ordihydrogenphosphates, and the corresponding phosphonates. It is alsopossible to use mixed salts of magnesium phosphate or magnesiumphosphonate with other salts, as for example with ammonium compounds,alkali metal compounds, or alkaline earth metal compounds. Examples ofsuch compounds are ammonium magnesium phosphate or sodium magnesiumphosphate.

In one preferred embodiment of the method of the invention, component(A) is at least one alkene selected from the group consisting of ethene,propene, 1-butene, 2-butene, 1-pentene, 1-hexene, 1-heptene, and1-octene.

In another preferred embodiment of the method of the invention, theacidic group in (B) is at least one group selected from the groupconsisting of carboxyl groups, sulfonic acid groups, and phosphonic acidgroups.

More preferably component (A) is ethene and component (B) is(meth)acrylic acid.

In one preferred embodiment of the method of the invention, 0.5 to 50mol % of the acid groups present in the copolymer are present in theform of neutralized groups. This neutralization is accomplishedpreferably by dispersing the polymer in the solvent with addition of thebase at an elevated temperature.

Bases used are typically one or more substances having a basic action,examples being hydroxides and/or carbonates and/or hydrogencarbonates ofalkali metals, or, preferably, amines such as ammonia, for example, andorganic amines such as alkylamines, N-alkylethanolamines, alkanolamines,and polyamines, for example.

Examples of alkylamines include the following: triethylamine,diethylamine, ethylamine, trimethylamine, dimethylamine, methylamine.Preferred amines are monoalkanolamines, N,N-dialkylalkanolamines,N-alkylalkanolamines, dialkanolamines, N-alkylalkanolamines andtrialkanolamines having in each case 2 to 18 C atoms in the hydroxyalkylradical and optionally in each case 1 to 6 C atoms in the alkyl radical,preferably 2 to 6 C atoms in the alkanol radical and optionally 1 or 2 Catoms in the alkyl radical. Especially preferred are ethanolamine,diethanolamine, triethanolamine, methyldiethanolamine,n-butyldiethanolamine, N,N-dimethylethanolamine, and2-amino-2-methylpropan-1-ol. Especially preferred are ammonia andN,N-dimethylethanolamine. Examples of polyamines that may be mentionedinclude the following: ethylenediamine, tetramethylethylenediamine(TMEDA), diethylenetriamine, and triethylenetetramine.

The copolymers are prepared by methods known to the skilled person. Forexample, the copolymers are prepared in accordance with the methodsdescribed in WO 2004/108601 A1.

The mixtures of copolymer and aqueous solvent mixture are prepared bymethods known to the skilled person. For example, the copolymer isdispersed in the solvent mixture produced by mixing beforehand.

In the context of the method of the invention it is preferred to use thecopolymer in the form of a formulation with water or with an aqueoussolvent mixture comprising least 75 weight % water. It is particularlypreferred in this case for the copolymer to be formulated only in wateras solvent, and for the concentration of the copolymer to be 0.5 to 50weight %, relative to the sum of all the components of the formulation.

The aqueous copolymer dispersions in the method of the invention areapplied preferably by means of injecting, spraying, dipping,spread-coating, or electrophoretic painting.

The method of the invention can be used to coat a multiplicity ofmetallic surfaces. The metallic surface preferably comprises a metalselected from the group consisting of Mg, Al, steel, Zn, and steelcoated with Zn, Al, Ni, Sn, Cr, or alloys thereof; more preferably themetallic surface comprises the metal Zn.

In another embodiment of the method of the invention, the aqueouscopolymer dispersion is contacted with an intermediate coat, theintermediate coat being in contact with the metallic surface. Theintermediate coat is preferably a conversion coat which serves topassivate the metal surface. Examples of such coats are Cr conversioncoats, phosphation coats, polymer-based aftertreatments, passivatingcoats comprising Ti compounds or Zr compounds, metal oxide coats,layer-by-layer coats, silane-crosslinked coats or oils, especiallyanticorrosion oils. The intermediate coat is preferably a Cr conversioncoat. These conversion coats are generated, as the skilled person isaware, from acidic (pH 0.5 to 5) Cr(III)- or Cr(VI)-containing solutionswhich include an oxidizing agent (such as NO₃—). The Zn surface here isminimally dissolved, and the consequent pH increase at the surface isaccompanied by the formation of a Cr- and Zn-containingoxidic/hydroxidic network which, according to application parameters(temperature, solution pH, application time) has a coat thickness of 20nm to 2 μm. The chromating, chromiting or passivating coats, as they arecalled, are known from the prior art (US19810265487, DE19638176A). It isalso possible to remove some or all of the intermediate coat prior totreatment with the aqueous copolymer dispersion, such removal takingplace for example in an alkaline cleaning bath. Oiled substrates whichhave not been degreased or have been only partly degreased may betreated directly with the copolymer dispersion by the method of theinvention.

In a further embodiment of the method of the invention, copolymerdispersions comprise, as a further component, film formers, crosslinkingcomponents, wetting agents, or other corrosion inhibitors different fromthe copolymers.

The copolymer dispersions may additionally, as described above, beadmixed with film-forming assistants. The latter may be solvents orsolvent mixtures, especially those having an evaporation numberaccording to DIN 53170 in the 50-20 000 range, examples being butylglycol or butyl diglycol. It is also possible, however, to addnon-evaporating compounds, especially alcohols which have been reactedwith alkylene oxides, more particularly ethylene oxide and/or propyleneoxide. These alcohols may be monohydric or polyhydric. These compoundsmay result in better spreading of the solution on the metal surface. Usemay also be made of alkoxylates of oligomeric or polymeric alcohols,such as of silicone derivatives, for example.

The addition of further components is possible as describedabove—examples are crosslinking components such as various siliconcompounds, nanoparticles, components with epoxy and/or isocyanategroups, and also corrosion inhibitors differing from the copolymers.Examples of suitable silicon compounds are silyl ethers and silanols ofthe formula Y,X—SiOR)_(3—x), where X and Y are any desired organicradicals, R is H or alkyl, and x is 0 or 1. These compounds may also benanoparticulate dispersions or oligomeric compounds that have alreadyundergone preliminary condensation.

Wetting agents as well may—as described above—be added to the copolymerdispersions. Examples of suitable wetting agents are nonionic, anionic,or cationic surfactants, more particularly ethoxylation and/orpropoxylation products of fatty alcohols, or propylene oxide-ethyleneoxide block copolymers, ethoxylated or propoxylated fatty alcohols oroxo-process alcohols, and also ethoxylates of oleic acid oralkylphenols, alkylphenol ether sulfates, alkylpolyglycosides,alkylphosphonates, alkylphenylphosphonates, alkyl phosphates, oralkylphenyl phosphates. Further examples are, in particular,polyethoxylated C₁₀-C₃₀ fatty alcohols or polyethoxylated C₁₁-C₃₁oxo-process alcohols.

Preference is given to using low-foam wetting agents, examples beingendgroup-capped ethoxylation and/or propoxylation products of fattyalcohols, where the alcoholic end group has been reacted to give anether, a methyl ether or ethyl ether, for example.

Particularly preferred wetting agents are alkoxylated fatty alcohols ofthe formula (I)

R¹—(OCH₂CHR²)_(x)(OCH₂CHR³)_(y)—OR⁴   (I)

where

-   -   R¹ is C₆-C₂₄ alkyl, linear or branched,    -   R² and R³ are H or C₁-C₁₆ alkyl, linear or branched,    -   R⁴ is H or C₁-C₈ alkyl, linear or branched,    -   x is an integer from the range from 1 to 200, and    -   y is an integer from the range from 0 to 80.

The alkylene oxide units in formula (I) may be arranged in one or moreblocks or randomly.

The present invention further provides a copolymer-coated metallicsurface obtainable according to any embodiment of the method of theinvention.

Generally speaking, the thickness of the copolymer-containing layer onthe metallic surface is from 0.1 to 30 μm, preferably from 0.2 to 30 μm,more preferably from 0.5 to 10 μm, very preferably from 1 to 6 μm.

In one embodiment of the coated metallic surface of the invention thereare also one or more paint layers, applied one above another, present onthe copolymer-containing layer.

In general the coated metallic surfaces may take on any desired form.The metallic surfaces are preferably surfaces of shaped or sheetlikebodies, more preferably the surface of coils, wires, tubes, panels,workpieces, shaped parts, joined parts and/or connected parts.

The copolymer dispersions may be applied to sheetlike or shaped metalsurfaces, as for example to coils, wires, and tubes, or to other shapedor sheetlike bodies.

When shaped bodies are used, the copolymer dispersions are appliedpreferably by dipping or spraying methods. After drying in this case,the applied films have a preferred average coat thickness in the rangefrom 0.2 to 30 μm, more particularly from 0.5 to 10 μm, very preferablyfrom 1 to 6 μm.

Drying may take place by various methods. In many cases, conventionaldrying at slightly elevated temperature is sufficient. The workpieces(shaped or sheetlike bodies) are preferably stored in an oven at 80° C.for 5 to 20 minutes. As and when necessary, however, higher temperaturesand longer or shorter times may be arranged.

A further subject of the present invention is the use of aqueouscopolymer dispersions comprising an effective amount of magnesium ionsand phosphate or phosphonate ions, or mixtures of phosphate andphosphonate ions, the copolymers present in the dispersion beingconstructed from the following components:

-   -   (A) from 20 to 95 weight % of monoethylenically unsaturated        hydrocarbons and/or hydrocarbons having two conjugated double        bonds,    -   (B) from 5 to 80 weight % of monoethylenically unsaturated        monomers which contain acid groups, and/or anhydrides or salts        thereof        to coat metallic surfaces.

Here, the amount of components (A) and (B) is based on the total amountof components (A) and (B). The total amount of components (A) and (B)here is 100 weight %. The components (A) are present preferably in therange from 20 to 95 weight % and (B) in the range from 5 to 50 weight %.

In one preferred embodiment of the use in accordance with the invention,the copolymers present in the dispersion comprise as a furthercomponent:

-   -   (C) from 0 to 30 weight % of ethylenically unsaturated monomers        different from (A) and (B).

The total amount of magnesium ions, phosphate ions, and phosphonate ionshere is in the range from 0.1 to 5 weight %, based on the amount ofcopolymers, preferably in the range from 0.2 to 3.5%, more preferably inthe range from 0.4 to 2 weight %, very preferably from 0.6 to 1.6 weight%.

In the context of use in accordance with the invention, the aqueouscopolymer dispersions are preferably contacted with an intermediatecoat, the intermediate coat being in contact with the metallic surface.

In a further embodiment of the method of the invention, the aqueouscopolymer dispersions comprise further additives as an additionalcomponent. Preferred further additives used are dispersants, dispersingassistants and/or wetting agents.

Examples of dispersants are polyacrylic acids or polyacrylic acidcopolymers. These polyacrylic acids or polyacrylic acid copolymers arepreferably in the form of their sodium salts. Further preferred aredispersants having a molecular weight Mw (weight average) of 1000 to 30000 g/mol, more particularly of 2000 g/mol to 10 000 g/mol. The totalamount of dispersant is from 0.01 to 1 weight %, based on the amount ofcopolymers in the aqueous copolymer dispersion. Preferably from 0.01 to0.2 weight % is used.

The use of dispersants in the aqueous copolymer dispersion leads to asurprising improvement in the storage stability.

Examples of dispersing assistants are surfactants. The total amount ofdispersing assistant is from 0.01 to 0.1 weight %, based on the amountof copolymers in the aqueous copolymer dispersion.

Examples of wetting agents are nonionic surfactants. The total amount ofwetting agent is from 0.01 to 0.1 weight %, based on the amount ofcopolymers in the aqueous copolymer dispersion.

With particular preference in the context of the use in accordance withthe invention, the coatings are used as what are called sealers, with aCr conversion coat acting as an intermediate coat. The sealer in thiscase leads to a distinct improvement in the corrosion control propertiesof the Cr conversion coat.

The present invention provides improved methods for the treatment ofmetallic surfaces, which can be employed with particular advantage inthe passivation of surfaces comprising steel and/or zinc orzinc-containing alloys.

The invention is illustrated by the examples, without the examplesrestricting the subject matter of the invention.

EXAMPLES

Polymer A:

An aqueous solution of 21 weight % (based on the amount of water) of acopolymer of ethylene and acrylic acid in a 70:30 weight ratio, having amolecular weight of approximately 30 000 D, and 3.5 weight % of the basedimethylethanolamine (based on the amount of water).

Polymer B:

An aqueous solution of 21 weight % (based on the amount of water) of acopolymer of ethylene and methacrylic acid in a 73:27 weight ratio,having a molecular weight of approximately 90 000 D, and 3.5 weight % ofthe base dimethylethanolamine (based on the amount of water).

Examples 1-11

Additive A:

Additive 1: magnesium phosphate octahydrate

Additive 2: magnesium methanesulfonate

Additive 3: magnesium acetate

Additive 4: di-sodium hydrogenphosphate

The corresponding additives 1 to 4 were added to the solution of thepolymers, and the solutions were then stirred for at least 3 hours.

The amount of the selected additive in weight % is based on the amountof copolymer used.

The aqueous preparations were adjusted to a copolymer concentration of20 weight %, based on the total amount of the preparation, by additionof the corresponding amount of water.

Oiled galvanized metal panels (dimensions about 220 mm*10 mm*0.5 mm, Znadd-on 100 g/m²) were immersed in ethyl acetate for around 1 minute andthen rubbed down with a paper towel.

They were then placed for 30 seconds at 60° C. in a bath of an alkalinecleaning solution (SurTec® 133 from Surtec Oberflächentechnik,Zwingenberg, Germany, 4% strength).

After that they were immersed 2 to 3 times into a bath containing mainswater at 60° C., and then into a bath containing fully demineralizedwater, then allowed to drip dry, and blown off with compressed air.

The dry metal panels were coated by doctor-blade application of thepolymer solutions. The doctor blades in this case were selected so as toproduce a wet film thickness of 12 μm. The metal panels weresubsequently dried in a forced-air drying oven (about 12 seconds, PMT(peak metal temperature) 50° C.), and then stored in a drying oven at80° C. for 10 minutes.

After 48 hours of storage in the laboratory, the metal panels weresubjected to a neutral salt spray mist test in accordance with DIN ENISO 9227. The degree of corrosion control RI24, according to EN ISO10289:2001, was ascertained after 24 hours. The results are summarizedin Table 1.

TABLE 1 Amount of additive Example Polymer Additive A A (weight %) RI24Comparative A 3 example 1 1 A 1 0.8 10 2 A 1 1.2 10 3 A 2 4 2 4 A 3 4 05 A 4 1.6 9 Comparative B 2 example 2 5 B 1 0.8 6 6 B 1 1.2 8 7 B 1 1.710 8 B 1 3 6 9 B 2 4 5 10  B 3 4 2 11  B 4 1.7 3

The examples show the advantageous corrosion control produced by addingmagnesium phosphate. The amount of additive A is based on the amount ofcopolymer.

The corrosion control provided by the preparations can in many casesalso be enhanced by magnesium ions or phosphates which originate fromother compounds of these ions. Nevertheless, the increase in corrosionresistance often turns out to be somewhat lower than when usingmagnesium phosphate (octahydrate).

Examples 12-16

The copolymers specified above can also be applied by means of immersionmethods. In that case the substrates used were hot-dip galvanized andelectrolytically galvanized metal test panels. The galvanized metalpanels were pretreated as described above and then immersed in copolymeremulsions at different concentrations, with different immersion timesand multiple immersion being investigated.

Polymer B was diluted with water to a copolymer concentration of 12weight %, and immersed twice. The drip-dry time between the immersionsteps was 1 minute.

Results (substrates):

-   -   a) application to electrolytically galvanized substrates:    -   b) application to electrolytically galvanized and Cr(III)        passivated/chromited substrates:

Results after neutral salt spray mist test in accordance with DIN EN ISO9227 (Table 2).

TABLE 2 Addi- Amount of Poly- tive additive A Example mer A (weight %)Substrate CA(24) C(28 d) Comparative B a) 100 example 3 12 B 1 1.6 a) 15Comparative B — — b) 7 example 4 13 B 1 1.6 b) <3 CA(24): corroded areain % of exposed metal panel area after 24 hours C(28 d): corroded areain % of exposed metal panel area after 28 days The amount of additive Ais based on the amount of copolymer.

A very great advantage is the fact that the copolymers can be formulatedwith a nonionic surfactant (e.g., Plurafac LF 300—alkoxylated fattyalcohol) without severe detriment to the corrosion control.Additionally, as a result, the visual appearance (very uniform withoutedges) and the mechanical properties (thinner polymer coat about 3 g/m²with wetting agent versus about 6 g/m² without wetting agent) ofsealing, in the case of immersion application, are massively improved.

Polymer B was admixed with the wetting agent Plurafac LF 300(alkoxylated fatty alcohol) and also, optionally, with 1.6 weight %(based on the amount of copolymer) of additive 1. The results aresummarized in Table 3.

TABLE 3 Wetting Additive 1 agent Add-on Example Substrate (weight %)(weight %) KF(24) KF(28 d) (g/m²) Comparative a) 1.0 10 4.0 example 5 14a) 1.6 1.0 7 2.9 Comparative b) — 1.0 25 4.1 example 6 15 b) 1 1.0 133.1 16 b) 1 0.1 10 3.1 CA(24): corroded area in % of exposed metal panelarea after 24 hours C(28 d): corroded area in % of exposed metal panelarea after 28 days The amount of additive 1 is based on the amount ofcopolymer. The amount of wetting agent is based on the amount of polymerB.

In the presence of the wetting agents, the films obtained with thecomposition of the invention were thinner relative to the comparativesystem, exhibiting a higher corrosion control in the neutral salt spraymist test in accordance with DIN EN ISO 9227.

Example 17

Using the solution from example 7, experiments were conducted on thestorage stability of the aqueous copolymer solutions. The experimentswere conducted over a period of 3 months each at temperatures of 10, 20,or 60° C. The stability of the solutions was evaluated by means ofvisual inspection. An unstable solution was apparent through gelformation at the surface of the solution.

TABLE 4 Results of stability test Time of Dispersant Temperature [° C.]gel formation 10 — 20 after one month 60 after one week Polyacrylic acid10 — Polyacrylic acid 20 — Polyacrylic acid 60 —

The polyacrylic acid employed was the sodium salt of a low molecularmass polyacrylic acid with a weight average of 4000 g/mol (Sokalan® CP10 from BASF SE). The concentration of the polyacrylic acid was 0.05weight %, based on the copolymers of example 7.

Using a dispersant reliably prevents gel formation even at elevatedtemperatures.

1. A method for coating a metallic surface, the method comprising:bringing the metallic surface into contact with an aqueous copolymerdispersion, wherein the aqueous copolymer dispersion comprises anaqueous copolymer, a magnesium ion and a phosphate or phosphonate ion,wherein the aqueous copolymer comprises: (A) from 20 to 95 weight % of amonoethylenically unsaturated hydrocarbon and/or a hydrocarbon havingtwo conjugated double bonds, (B) from 5 to 80 weight % of amonoethylenically unsaturated monomer comprising an acid group, and/oran anhydride or a salt thereof.
 2. The method according to claim 1,wherein the aqueous copolymer further comprises: (C) from 0 to 30 weight% of an ethylenically unsaturated monomer different from components (A)and (B).
 3. The method according to claim 1, wherein a total amount ofthe magnesium ion, a phosphate ion, and a phosphonate ion is from 0.1 to5 weight %, based on an amount of the aqueous copolymer.
 4. The methodaccording to claim 1, wherein component (A) is at least one alkeneselected from the group consisting of ethene, propene, 1-butene,2-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.
 5. The methodaccording to claim 1, wherein the acid group is at least one groupselected from the group consisting of a carboxyl group, a sulfonic acidgroup, and a phosphonic acid group.
 6. The method according to claim 1,wherein 0.5 to 50 mol % of an acid group in the aqueous copolymer isneutralized.
 7. The method according to claim 1, further comprising:applying the aqueous copolymer by spraying, injecting, dipping,spread-coating or electrophoretic painting.
 8. The method according toclaim 1, wherein a metal in the metallic surface is one selected fromthe group consisting of Mg, Al, steel, Zn, and a steel coated with Zn,Al, Ni, Sn, Cr, or an alloy thereof.
 9. The method according to claim 1,further comprising: contacting the aqueous copolymer dispersion with anintermediate coat, wherein the intermediate coat is in contact with themetallic surface.
 10. The method according to claim 9, wherein theintermediate coat is a Cr conversion coat.
 11. The method according toclaim 1, wherein the aqueous copolymer dispersion further comprises afilm-former, a crosslinking component, a wetting agent, or a corrosioninhibitor different from the aqueous copolymer.
 12. A copolymer-coatedmetallic surface obtainable by the method according to claim
 1. 13. Thecoated metallic surface according to claim 12, comprising: one or morepaint coats applied one over another located on a copolymer-containingcoat.
 14. An aqueous copolymer dispersion comprising: an aqueouscopolymer, a magnesium ion and a phosphate or phosphonate ion, whereinthe aqueous copolymer comprises: (A) from 20 to 95 weight % of amonoethylenically unsaturated hydrocarbon and/or a hydrocarbon havingtwo conjugated double bonds, (B) from 5 to 80 weight % of amonoethylenically unsaturated monomer comprising an acid group, and/oran anhydride or a salt thereof.
 15. The aqueous copolymer dispersionaccording to claim 13, wherein the aqueous copolymer dispersion isbrought into contact with an intermediate coat, and the intermediatecoat is in contact with the metallic surface.